Products such as produce, meat and the like being shipped relatively long distances are conventionally placed within refrigerated containers specifically designed for maintaining a desired temperature of such products for an extended period of time. Such containers are typically found on shipboard for sea transport and sometimes utilized for overland shipment by rail. The containers are portable; that is, they are transported from a loading facility such as dock side to a moored vessel and removed from the vessel at the destination port. The containers are frequently secured to flatbed cars for rail shipment and flatbed chassis for highway shipment and are temporarily stored at the shipping and receiving ends of the voyage.
The demands on such refrigerated containers are severe in view of the variety of climatic conditions to which the containers are subjected as well as the abusive handling frequently encountered during loading and unloading procedures.
Prior art refrigerated containers were typically constructed of lightweight materials such as aluminum and included appropriate insulation to permit the inside temperature to be maintained at a desired level. Electrical refrigeration systems were usually attached to the front of such containers as a package to be powered by shipboard electrical supply. In many instances, when the container was being transported by a facility not having an electrical power supply, or when the container is being stored in a loaded condition at a facility not having electrical power, a local electrical generator powered by a diesel engine was mounted or attached to the container and provided with a limited fuel supply to permit the container to maintain its desired internal temperature.
The cooling refrigerated air within the container was usually circulated through the utilization of fans which directed the air from the front of the container to the rear over the contents to attempt to maintain an uniform temperature of all products within the container. The circulation of cool air within the container sometimes was impeded by the configuration and density of the container contents which in turn created significant static back pressure on the fans. The reduction or blockage of airflow and the distance over which the cool air had to be blown, from twenty feet to forty-five feet depending upon the length of the container, resulted in substantial temperature variation and improper cooling of all of the products within the container as well as the consumption of an excessive amount of electrical power. The rough handling of such containers frequently resulted in significant damage to the container and sometimes to the contents. The attachment to or adding of a diesel driven electrical generator with fuel storage presented a cumbersome and inefficient utilization of the exterior volume occupied by the container during shipment; further, the addition of such equipment external to the container rendered such equipment susceptible to damage during handling of the container which, in turn, resulted in damage to the products within the container caused by improper refrigeration.
The refrigeration systems of such prior art refrigerated containers utilize control systems typical of refrigeration systems used in cold storage facilities; that is, evaporator coils were defrosted to remove accumulated ice in response to one or more of a variety of parameters such as reduced airflow through evaporator coils. The sensor systems utilized to detect the above parameters were usually elaborate and very expensive; further, the requirement that such systems be absolutely reliable dictated redundancy in view of the inherent complexity which resulted in further cost.